A dynamo-electric machine includes a rotor, a stator, a bearing, and a frame, and hydrogen gas is sealed as a coolant gas in the dynamo-electric machine. A shaft sealing device is provided at the bearing such that the coolant gas does not leak from the bearing. Sealing oil having a pressure higher than internal pressure of the dynamo-electric machine is supplied to the shaft sealing device through a sealing oil supply line. The sealing oil discharged from the shaft sealing device is collected and returned to the sealing oil supply line. The sealing oil, which flows and is discharged onto an air side of the bearing from the shaft sealing device, contains Gases, such as air. When the collected oil is circulated to the sealing oil supply line, the gases are dissolved from the sealing oil to gradually degrade purity of the hydrogen gas in the frame.
There are well known two systems that are provided in the sealing oil supply line in order to maintain the purity of the hydrogen gas. One of the systems is a vacuum treatment system in which the sealing oil supplied to the shaft sealing device is degassed with a vacuum treatment apparatus, and the other is a continuous scavenging system in which not the vacuum treatment apparatus but equipment is provided in order to maintain the purity of the hydrogen gas in the dynamo-electric machine.
For the gas purity maintainer in which the continuous scavenging system is adopted, the purity of the hydrogen gas in the dynamo-electric machine is gradually degraded because the sealing oil to which a vacuum treatment is not performed is supplied to the shaft seal device. Therefore, the purity of the gas is maintained by automatically supplying the new hydrogen gas having the high purity while a given amount of gas is continuously scavenged.
When the coolant gas is scavenged from a sealing oil treatment system by the continuous scavenging system in order to maintain the purity of the hydrogen gas that is of the coolant gas in the dynamo-electric machine, part of the sealing oil becomes mist having a fine particle size, and is mixed in the scavenged coolant gas. When the mist of the sealing oil is mixed in the scavenged coolant gas, the mist of the sealing oil adheres in the middle of the piping which transports the coolant gas, and returns to a liquid. The liquid of the sealing oil is accumulated in the piping. A needle valve that controls a scavenging flow rate and the pressure and an instrument panel in which gauges, such as a flowmeter and a purity meter, are placed are connected in the middle of the coolant gas scavenging piping. The flowmeter measures the scavenging flow rate, and the purity meter measures the purity of the hydrogen gas that is of the scavenged gas.
Particularly, when the mist invades in the needle valve and the gauges of the instrument panel, the liquid sealing oil is easily accumulated due to structures of the needle valve and the gauges. As a result, an error is generated in the flow rate controlled by the needle valve, or errors are generated in displays of the gauges. When the error is generated in the flow rate controlled by the needle valve, the scavenging flow rate of the coolant gas is decreases to degrade the purity of the hydrogen gas that is of the coolant gas. When the errors are included in the displays of the gauges, continuous scavenging operation cannot properly be performed because normal monitoring is not performed.